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Comparative Evaluation of Bidirectional Dual Active Bridge DC-DC Converter Variants
... A structure using half-and fullbridge topologies with both I-type primary and I-type secondary side of the transformer has also been studied in [19,20] that examine the control strategy and zero voltage switching (ZVS) of these topologies. In addition, the other structures have also been studied in the literature which are T-type only in the primary side of the transformer in [21] and T-type only in the secondary side of the transformer in [22][23][24]. Also, T-type switching combination topologies are stated in [24] as more efficient topology than I-type. ...
... In addition, the other structures have also been studied in the literature which are T-type only in the primary side of the transformer in [21] and T-type only in the secondary side of the transformer in [22][23][24]. Also, T-type switching combination topologies are stated in [24] as more efficient topology than I-type. ...
... Furthermore, the measured efficiency of the prototype is 96.27% at full load condition. The peak efficiencies of 94.8% at 2.8 kW [24], 95.5% at 1.2 kW [25], 96.5% at 1.2 kW [26], 96.71% at 1 kW [16] can be found in the literature of three-level isolated bidirectional DC-DC converters. Therefore, the proposed 3LTT-IBDC seems more promising in terms of achieving high efficiency. ...
This study presents a novel three-level T-type isolated bidirectional DC–DC converter (3LTT-IBDC) for bidirectional
DC power transfer. Owing to of the T-type structure of the proposed converter it has less number of switches and thus, lower
cost and higher efficiency, as well as easy control are the advantages of the proposed converter compared to three-level
counterparts. Additionally, 3LTT-IBDC is more reliable than three-level converters since unequal voltage blocking does not occur
in T-type structure. Moreover, the symmetrical operation of the isolation transformer due to three-level symmetrical voltage
waveform, lower voltage stress of switches and thus, higher efficiency are other advantages of 3LTT-IBDC compared to twolevel
counterparts. Here, the DC voltage gain and power transfer characteristic of the proposed converter for steady-state
operation and the expressions of the leakage inductance are derived. The proposed converter is simulated using PSIM. A 2-kW
prototype is built to verify the theoretical analysis of the converter. Theoretical and experimental results show a good agreement
and validate the competency of the presented converter design. The efficiency of the proposed converter and switching
transitions of the switches are analysed. The full load and maximum efficiency of the converter are measured as 96.27% and
96.81%, respectively.
... These topologies are capable of achieving high voltage attenuation. For variation in load power or input voltage variations, the duty cycle of the switches employed can be varied [18]. ...
... Another variant utilizing GaN devices and an integrated transformer is used for realizing the DAB converter, as shown in Fig. 20. Here, a partial parallel DAB converter is presented [18]. This converter achieves higher reliability and eliminates the need for any external inductors. ...
Ever-increasing digital connectivity coinciding with the advent of Industry 4.0 has significantly increased the need for reliable, safe, and fast-processing data centers. The reliability of these data centers depends on the continuity and quality of electrical power powering these centers. Although individual server racks are rated for a few kWs, their cumulative rating can reach MWs for typical data centers. Typically, these data centers are powered from medium voltage lines and require a rigid, efficient, and fast-responding power delivery architecture (PDA) to supply electronic loads operating at very low voltages. To achieve the desired performance, wide-bandgap (SiC/GaN)- based power-electronic converters operating at high frequencies provide a superior alternative to replace the existing Si-based power converters, improving the overall power density and operating efficiency. This paper presents a critical review of data centers' power delivery in general and on-board isolated DC-DC converters in particular. A detailed comparison of wide-bandgapbased-isolated DC-DC converters is presented considering the key features, efficiency, and power rating. Post-assessment, the potential opportunities for improving efficiency, power quality, and the subsequent impact of renewables on carbon footprint are also highlighted
... A symmetric modulation-based 3-5 Level multilevel DAB (MLDAB) having NPC as a secondary side with the capacitor voltage balancing has been presented in [19]. In [20], a detailed comparison of three different DAB topologies named as 3-3 Level HB-HB, 3-5 Level HB-NPC and 3-5 Level HB-T-type leg has been reported. It was concluded that 3-5 Level FB-T-type will be a good choice out of three topologies due to low AC-link losses and good utilisation of the semiconductor area. ...
To cater unceasing supply to the modern AC and DC loads, renewable energy resources integrated Hybrid DC/AC Micro Grid (HMG) are considered as a viable technological solution. In this paper, a Multiple Parallel connected Bidirectional Converter (MPBC) topology has been proposed to enhance the Solid State Transformer (SST) power handling capability with flexible control of the HMG. To improve the high frequency AC link power quality and to control the power transfer through the SST in each Dual Active Bridge (DAB) a split step phase shift (SSPS) control technique has been used. A power management control strategy has also been proposed for efficient power transfer between the sources and loads of the HMG. The proposed MPBC based SST is suitable for interconnecting multiple utility feeders. Multiple redundant utility feeders ensure stiff bus voltages and omit the power supply reliability issues. The operation of the proposed MPBC-SST converter system with corresponding control algorithm is verified through the simulation results in both grid feeding and grid fetching operating modes. Furthermore, experimental results are presented to validate the performance of the proposed MPBC-SST converter along with its proposed controller strategy.
... and minimize the output capacitance, by generating three-level AC voltages at the HFT terminals [108]. Another approach to generate three or five-level AC voltages is by replacing one of the full bridges by a multilevel bridge [109]. The possibility to operate in buck and boost mode associated with the high-efficiency and the fast dynamic response makes the DAB an attractive topology for bidirectional and isolated DC-DC power conversion. ...
The battery energy storage systems (BESS) need a bidirectional AC-DC power conversion system (PCS) to interface a battery pack with the electric power grid. The aim of this work is to increase the power density of the power electronics converter and keep simultaneously the same reliability of traditional solutions. These goals are pursued through the reduction of the conversion stages and utilization of design methodologies to reduce the volume of the passive components. The matrix converter is a key element of the system, since it performs a direct AC to AC conversion between the grid and the high-frequency transformer (HFT) dispensing the traditional DC-link capacitors. Therefore, the circuit volume and weight are reduced and a longer service life is expected when compared to the existing technical solutions. The interface between the HFT and the battery pack is then performed by a full-bridge (FB) converter. The resulting power circuit is the commonly known high-frequency link matrix converter (HFLMC). A new modulation for the HFLMC is proposed in this thesis featuring controllable power factor in the grid interface
as well as voltage and current regulation for a battery energy storage device.
A prototype was built to verify the feasibility and performance of the proposed modulation. An electromagnetic interference (EMI) filter for differential-mode and common-mode filtering was designed for compliance with CISPR 11 Class B standard. Regarding the magnetic components, analytic and software tools were employed for the optimized design of the high-frequency transformer and link-inductor. The control system is composed by a digital signal processor (DSP) plus a field-programmable gate array (FPGA) for the signal acquisition and generation of the sixteen command signals. Silicon carbide (SiC) MOSFETs are used in order to allow high switching frequency with low losses. The respective gate driver circuit was developed to allow safe and reliable commutations up to 100 kHz. This research was conducted in the Smart Grids and Electric Vehicles (SGEV) laboratory
of INESC TEC. The experimental tests show the capability to control the grid currents in the synchronous reference frame in order to provide grid services. Simultaneously, the battery current is well regulated with a small ripple which makes this converter suitable
for battery charging of electric vehicles and energy storage applications.
Direct current (dc) transformers are an important component of the multiterminal interconnected flexible dc distribution network. However, it is apt to suffer from the inrush current, which can trigger the shutdown protection and threaten the reliability of the system and equipment. In this article, a 2-MW dc transformer is developed for a T-connected star type multiterminal flexible dc distribution network, where the dual active bridge (DAB) converter is one of the important components. The design of the key parameters is also presented. Based on the steady-state model of the dc transformer, the overcurrent mechanism is elaborated and a suppression strategy of H-bridge temporary blocking and DAB not blocking is proposed, which can automatically clear the fault current. Simulations and practical engineering tests are conducted to verify the effectiveness and practicability of the proposed method, which provides engineering practical value.
Concerns about fuel exhaustion, electrical energy shortages, and global warming are growing due to the global energy crisis. Renewable energy-based distributed generators can assist in meeting rising energy demands. Micro-energy grids have become a research hotspot as a crucial interface for connecting the power produced by renewable energy resources-based distributed generators to the power system. The integration of micro-energy grid technology at the load level has been the focus of recent studies. Direct Current Micro-energy-grids have been one of the major research fields in recent years due to the inherent advantages of DC systems over AC systems, such as compatibility with renewable energy sources, storage devices, less losses, and modern loads. Nevertheless, control and stability of the grid are the paramount constituents for the reliable operation of power systems, whether at generation or load level. This research article focuses on the power flow between DC feeders of an autonomous DC micro-energy grid. To achieve this objective, a mathematical model and classical control strategy for power flow between two DC feeders are proposed using a conventional dual active bridge converter. The control objective is to minimize the DC element in the High-Frequency Transformer. Firstly, the non-linear-switched converter model and generalized average model for converter control are presented. Then, these mathematical models are used to get a small-signal linear model so a classical control strategy can be implemented. The control method enables output voltage regulation while abstaining from the high-frequency transformer's winding saturation. The stability analysis endorses the validity of the proposed control scheme. Also, the system response to load changes and varying control parameters is consistent. The simulation results validate the proposal's performance for changing converter and control parameters.
This paper gives a comprehensive comparison of multilevel high-frequency-link (HFL) dc transformer (abbreviated MDCT) based on modular multilevel converter (MMC) and multilevel-dc-link dc transformer (abbreviated ADCT) based on dual-active-bridge (DAB) for medium-voltage dc (MVDC) application. The topology, operation, HFL voltage and current, active and circulating power, characteristic currents, switching behaviors, and power loss are analyzed in detail. Both MDCT and ADCT have fault treatment ability for MVDC application. However, the installation and commissioning of ADCT are more flexible and simpler. In addition, the MDCT needs more switches and high-frequency inductors than ADCT in MVDC side with the same voltage level, but the number of high-frequency transformer can be reduced. Compared with MDCT, the ADCT has higher power transfer ability and lower circulating power, then it has lower HFL voltage, and current RMS and peak values with the same transmission power in MVDC side. However, the arm RMS and average currents of MDCT are lower than those of ADCT in MVDC side. The switching performance of MDCT deteriorates when the MVDC voltage fluctuates, but the switching behaviors of half-bridges are added to ADCT. The loss of ADCT almost keep the same when the MVDC voltage fluctuates, but the loss of MDCT changes a lot. Finally, a small scale prototype platform with 1kW/450V/150V is built and experimental results verify the correctness and effectiveness of the theoretical analysis.
This paper presents a converter consisting of a dual active bridge built upon three-level neutral-point-clamped legs in order to synthesize a five-level medium- or high- frequency stepped waveform on each side of the transformer. Thanks to the modulation extra degrees of freedom, the transformer current harmonic content can be reduced (less magnetic losses) and the fundamental component of the transformer primary and secondary voltages can be adjusted to minimize the reactive power (less conduction losses). A modulation strategy and control scheme to regulate the dc-link capacitor voltage balance is proposed. The topology, modulation, and balancing control are validated through simulations.
An improved calculation of ferrite core loss for nonsinusoidal waveforms separates a flux trajectory into major and minor loops via a new recursive algorithm. It is highly accurate and outperforms two previous methods for our measured data. The only characteristics of the material required are the standard Steinmetz-equation parameters.
This paper details efficiency optimized operation and design of a bi-directional and isolated five-level Dual Active Bridge (5LDAB) converter for an application that requires ultra-wide voltage and power ranges. The rated power of the considered converter is 7.5kW, the specified input voltage range is 150V ≤ Vdc1 ≤ 800V and the output voltage is constant, Vdc2 = 700V. In order to achieve high efficiency levels in a wide operating range, a modulation scheme is proposed to minimize the transformer rms current. Results of transformer rms currents and of efficiencies are presented for the 5LDAB and compared with the results obtained for an efficiency optimized conventional Dual Active Bridge (DAB) converter. Compared with the DAB topology, the 5LDAB converter can achieve an overall reduction of transformer rms currents and of conduction losses in the higher voltage regime of the operating range.
A novel converter configuration that allows for high frequency transformer integration and high voltage distribution is proposed for large scale grid-connected photovoltaic (PV) system. The proposed configuration has in the front-end of the solar panel, dual-active bridge dc-dc converter with three-level neutral-point clamped secondary and a high-step-up ratio high frequency transformer. The output of the dual-active bridge converter may be connected to a high voltage inverter to achieve high ac voltage to allow for direct interconnection with the utility ac grid at distribution voltage level. The proposed configuration has advantages of high frequency transformer, high efficiency and high voltage operation. Phase-shift modulation technique along with Maximum Power Point Tracking is proposed for the three-level dual-active bridge converter and the overall converter performance is verified in simulation.
Dual Active Bridge (DAB) dc-dc converter finds applications in the intermediate high frequency link power conversion stage of a high-power solid state transformer. In this paper, a multilevel DAB dc-dc converter is proposed. A three-level neutral point clamped (NPC) inverter topology has been used in the high voltage bridge which enables semiconductor switches to be operated in higher voltage range without using cascaded bridges and multiple DAB converters. Modulation strategy to control power flow between the active bridges with one of the bridges switching at multi-level is proposed in this paper. Steady-state analysis of the converter with the proposed modulation scheme is presented along with simulation results to augment the analysis.
A comprehensive procedure for the derivation of optimal, full-operating-range zero voltage switching (ZVS) modulation schemes for single-phase, single-stage, bidirectional and isolated dual active bridge (DAB) ac–dc converters is presented. The converter topology consists of a DAB dc–dc converter, receiving a rectified ac line voltage via a synchronous rectifier. The DAB comprises primary and secondary side full bridges, linked by a high-frequency isolation transformer and a series inductor. ZVS modulation schemes previously proposed in the literature are either based on current-based or energy-based ZVS analyses. The procedure outlined in this paper for the calculation of optimal DAB modulation schemes (i.e., combined phase-shift, duty-cycle, and switching frequency modulation) relies on a novel, more accurate, current-dependent charge-based ZVS analysis, taking into account the amount of charge that is required to charge the nonlinear parasitic output capacitances of the switches during commutation. Thereby, the concept of “commutation inductance(s)” is shown to be an essential element in achieving full-operating-range ZVS. The proposed methods are applied to a 3.7 kW, bidirectional, and unity power factor electric vehicle battery charger which interfaces a 400 dc-bus with the , 50-Hz utility grid. Experimental results obtained from a high-power-density, high-efficiency converter prototype are given to validate the theoretical analysis and practical feasibility of the proposed strategy.
A new Dual Active Bridge (DAB) topology is proposed with a 15-kV SiC-IGBT based three-level inverter at the high-voltage side and 1200-V SiC-MOSFET based paralleled two-level inverter at the low-voltage side. The proposed DAB is an integral part of a solid state transformer which connects a 13.8-kV distribution grid and a 480-V utility grid. The three-level inverter connected at the high-voltage side and a pair of two-level inverters connected at the low-voltage sides (in Y/Δ) of the high frequency link transformer help to reduce dominant harmonic currents. Thus harmonic-free currents in the high frequency link transformer are achieved without pulse-width modulation. A simple control is proposed and validated with simulation results.
For realizing bidirectional and isolated AC/DC converters, soft-switching techniques/topologies seem to be a favourable choice as they enable a further loss and volume reduction of the system. Contrary to the traditional dual-stage approach, using a power factor corrector (PFC) stage in series with a DC/DC isolation stage, we showed recently that the same functionality can be achieved under full soft-switching operation using a single-stage dual active bridge (DAB) AC/DC converter. This paper investigates the performance of this single-stage approach by comparing it with a state-of-the-art conventional dual-stage concept (both soft-switching converters), where a bidirectional interleaved triangular current mode (TCM) PFC rectifier was chosen in combination with a DAB DC/DC converter. The advantages and drawbacks of each concept are discussed in detail, focusing on the impact of the utilized semiconductor technology and silicon area on the converter efficiency. Furthermore, a comprehensive comparison of power density is allowed by the analytical models that correlate the component losses with their respective volume.
A switching control strategy to enable Zero-Voltage-Switching (ZVS) over the entire input-voltage interval and the full power range of a single-stage Dual Active Bridge (DAB) AC/DC converter is proposed. The converter topology consists of a DAB DC/DC converter, receiving a rectified AC line voltage via a synchronous rectifier. The DAB comprises primary and secondary side full bridges, linked by a high-frequency isolation transformer and inductor. Using conventional control strategies, the soft-switching boundary conditions are exceeded at the higher voltage conversion ratios of the AC input interval. Recently we presented a novel pulse-width-modulation strategy to fully eliminate these boundaries, using a half bridge — full bridge DAB configuration. In this papers the analysis is extended towards a full bridge — full bridge DAB setup, providing more flexibility to minimize the component RMS currents and allowing increased performance (in terms of efficiency and volume). Experimental results are given to validate the theoretical analysis and practical feasibility of the proposed strategy.
An approach to accurately calculate the reluctance of an air gap is introduced. The approach is easy to handle as it is based on a modular concept where a simple basic geometry is used as a building block to describe different three dimensional air gap shapes. A high degree of accuracy is achieved as the approach is based on an analytical field solution.
In order to find the optimal converter topology for a given AC motor drive, as defined by its mission profile, suitable assessment criteria have to be applied. A new semiconductor chip area based approach is proposed to compare and assess different motor drive converter topologies. It determines the total semiconductor chip area based on the drive's operating point and the optimal partitioning of the transistor and diode chip areas. This approach not only provides a distinct figure-of-merit for comparison but also enables the semiconductor costs of different converter topologies to be determined. The chip area based comparison has been successfully used to assess three 3-phase AC-DC-AC converter topologies for a 15 kW (20 HP) motor drive. It is shown that the voltage DC-link back-to-back converter based drive provides the best overall performance in terms of chip area, cost, efficiency, and available nominal torque.
Loss models of inductive components are thoroughly investigated, thereby all different aspects of loss modeling are considered. The impact of peak-to-peak flux density ΔB, frequency f, DC premagnetization HDC, temperature T, core shape, minor and major loops, flux waveform, and material on core loss calculation are considered. In order to calculate winding losses, formulas for round conductors and litz wires, each including skin- and proximity effects (including the influence of an air-gap fringing field) are included. A high level of accuracy is achieved by combining the best state-of-the-art approaches and by embedding newly-developed approaches into a novel loss calculation framework. The loss models are verified by FEM simulations and experimental measurements.
A new modulation strategy that allows operating the dual active bridge (DAB) dc-dc converter under soft switching in the whole operating range is proposed. This strategy is ruled by imposing a certain modulation index in one of the two bridges and a phase shift between the transformer primary and secondary voltages. Moreover, the proposed algorithm reduces the reactive power and thus reducing the converter conduction losses. An experimental prototype was implemented and some experimental results are presented to validate the theoretical analysis. The experimental results reveal that the overall efficiency of the DAB topology can be improved up to 20% by implementing the proposed modulation strategy instead of the conventional one.
The authors present three DC/DC converter topologies suitable for high-power-density high-power applications. All three circuits operate in a soft-switched manner, making possible a reduction in device switching losses and an increase in switching frequency. The three-phase dual-bridge converter proposed is seen to have the most favorable characteristics. This converter consists of two three-phase inverter stages operating in a high frequency six-step mode. In contrast to existing single-phase AC-link DC/DC converters, low RMS current ratings are obtained for both the input and output filter capacitors. This is in addition to smaller filter element values due to the higher-frequency content of the input and output waveforms. The use of a three-phase symmetrical transformer instead of single-phase transformers and a better utilization of the available apparent power of the transformer (as a consequence of the controlled output inverter) significantly increase the power density attainable
Three DC/DC converter topologies suitable for high-power-density
high-power applications are presented. All three circuits operate in a
soft-switched manner, making possible a reduction in device switching
losses and an increase in switching frequency. The three-phase
dual-bridge converter proposed is shown to have the most favorable
characteristics. This converter consists of two three-phase inverter
stages operating in a high-frequency six-step mode. In contrast to
existing single-phase AC-link DC/DC converters, lower turn-off peak
currents in the power devices and lower RMS current ratings for both the
input and output filter capacitors are obtained. This is in addition to
smaller filter element values due to the higher-frequency content of the
input and output waveforms. Furthermore, the use of a three-phase
symmetrical transformer instead of single-phase transformers and a
better utilization of the available apparent power of the transformer
(as a consequence of the controlled output inverter) significantly
increase the power density attainable
Elektrischer Leistungswandler zur DC/DC-Wandlung mit Dualen Aktiven Brücken
- J Everts
- J W Kolar
Modeling and Optimization of Bidirectional Dual Active Bridge AC DC Converter Topologies
- J Everts